Method for operating a steering system

ABSTRACT

A method is described for operating a steering system ( 2 ) of a motor vehicle. A steering means ( 8 ) is connected to a steering gear ( 14 ) by means of an active steering system ( 4 ). During autonomous operation of the motor vehicle, a driver&#39;s intervention ( 40 ) in the steering means ( 8 ) is determined. The active steering system ( 4 ) is operated in such a way that a coupling ( 30 ) between an angle ( 26 ) of the steering means and an angle ( 28 ) input into the steering gear ( 14 ) is adjusted depending on the thus determined driver&#39;s intervention ( 40 ).

BACKGROUND OF THE INVENTION

The invention relates to a method for operating a steering system of amotor vehicle.

It is known that the use of driver assistance systems and drivingfunctions which permit the highly autonomous or fully autonomous drivingof a motor vehicle always also have to provide the possibility oftransferring the control over the vehicle to the driver of the vehicle.If the driver of the vehicle has control over the vehicle, possibilitiesmust be made available for changing back into the autonomous drivingmode.

Furthermore, steering systems are known which have both asuperimposition steering system and a power steering system. Thesuperimposition steering system is also referred to as active steering(AFS=Active Front Steering) and brings about an angle superimposition.The power steering system is also referred to as servo steering and canbe a hydraulic steering system or an electromechanical steering system(EPS=Electric Power Steering). The power steering system brings about atorque superimposition in a driving mode in which the driver is assistedin his driving request or steering request.

Functions and sensors are also known which detect a driver interventioninto a steering means.

SUMMARY OF THE INVENTION

The problem on which the invention is based is solved by a method.Important features for the invention can also be found in the followingdescription and in the drawings, wherein the features can be importantfor the invention either alone or in different combinations, withoutreference being explicitly made thereto once more.

By virtue of the fact that a superimposition steering system is operatedin such a way that a coupling between a steering means angle and anangle which is introduced into a steering gear is adjusted as a functionof a driver intervention detected during an autonomous driving mode ofthe motor vehicle it is advantageously ensured that the driver alone canhimself determine, through the active operation of the steering means,for example in the form of a steering wheel, how much control he wouldlike to have over the steering system and therefore over the motorvehicle. In the case of an autonomous driving mode with an activeautonomous steering function, a harmonious transfer between the driverand the steering function can therefore be made possible.

In one advantageous refinement of the method, the influence of anautonomous steering function on the wheel steering angle is determinedas a function of the detected driver intervention. This permits theautonomous steering function to be used selectively to implement theharmonious transfer between the driver and the autonomous steeringfunction.

In one advantageous embodiment, the coupling is increased as a functionof an increasing or essentially consistently elevated driverintervention. The driver of the vehicle is therefore advantageouslyprovided with more control over the steering system and therefore morecontrol over the wheel steering angle.

In one advantageous development, the influence of the steering functionon the wheel steering angle is reduced as a function of an increasing oressentially constant increased driver intervention. This measureincreases further the control of the driver of the vehicle over thewheel steering angle of the steering system.

In one advantageous development of the method, at a first time theincreasing or essentially constant increased driver intervention isdetected. Starting from the first time, the coupling is increased up toa second time and/or the influence of the autonomous steering functionon the wheel steering angle is reduced in such a way that at or afterthe second time the autonomous steering function can be deactivated oris deactivated. This provides a method with which the driver of themotor vehicle can be forced, within a determined time period, to assumethe control over the vehicle. For example in a situation in which theautonomous steering function is faulty or another sub-system has afault, the control over the vehicle must be transferred to the driver ofthe vehicle.

In one advantageous embodiment, the coupling is reduced as a function ofa reducing driver intervention. Therefore, the autonomous steeringfunction can assume the control over the vehicle, for example, as soonas the driver takes his hands off the steering means or the steeringwheel or else the driver would like to give up the control over thevehicle by means of a separate signaling means.

In one advantageous embodiment, the influence of the autonomous steeringfunction on the wheel steering angle is increased as a function of areducing driver intervention.

In one advantageous embodiment, at a third time the reducing driverintervention is detected. Starting from the third time up to a fourthtime the coupling is then reduced and/or the influence of the autonomoussteering function on the wheel steering angle is increased in such a waythat at or after the third time the steering function has completecontrol over the steering system. Therefore, time periods can be definedwhich permit, for example, a harmonious transfer of the control to theautonomous steering function in the case of a reducing driverintervention, for example as a function of the vehicle speed or othervariables.

In one advantageous embodiment, the coupling is adjusted as a functionof a current and/or planned setpoint torque input into the steeringgear, which input is detected by the autonomous steering function. Forexample in the case of highly transient changes in torque, for examplewhen traveling through a roundabout, it is therefore advantageouslypossible for the coupling to remain reduced, as a function of theplanned high setpoint torque input, to such an extent that a risk ofinjury by a rotating steering wheel to which a torque is applied by theservo steering is reduced. On the other hand, the coupling can beadjusted to such a high setting that even in the case of travel througha roundabout with a corresponding input of torque into the steering gearan avoidance maneuver is still possible by the driver.

In one advantageous embodiment, in the case of an increased vehiclespeed the time period between the first time and the second time and/orthe time period between the third time and the fourth time is selectedto be longer than in the case of a reduced vehicle speed. This makes itpossible to ensure that the control over the steering system istransferred between the driver and the autonomous driving function inaccordance with the driving situation.

In a further advantageous embodiment a differentiation is made betweenan intended driver intervention and an unintended driver intervention.In the case of an intended driver intervention the coupling is increasedor maintained. In the case of an unintended driver intervention thecoupling is reduced. It is therefore possible, for example, on the onehand to reduce the risk of injury by an input of torque into thesteering means by a power steering system. On the other hand, advantagesare obtained in respect of the transfer to or from the autonomoussteering function.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, application possibilities and advantages of theinvention can be found in the following description of exemplaryembodiments of the invention which are illustrated in the figures of thedrawing. In this context, all the features which are described orillustrated form, per se or in any desired combination, the subjectmatter of the invention independently of their combination in the patentclaims or their back-reference and independently of their formulation orpresentation in the description or in the drawing. In some cases thesame reference symbols are also used for different embodiments, withouta restriction arising directly from this. The exemplary embodiments ofthe invention are explained below with reference to the drawing. In thedrawing:

FIG. 1 shows a schematically illustrated steering system;

FIG. 2 shows a state transition diagram; and

FIG. 3 shows a schematic relationship between an influence of theautonomous driving function on a wheel steering angle and a driverintervention.

DETAILED DESCRIPTION

FIG. 1 shows a steering system 2 in schematic form. The steering system2 comprises a superimposition steering system 4 and a power steeringsystem 6. A steering means 8, for example a steering wheel, is connectedto the superimposition steering system 4 via an input shaft 10 of thesuperimposition steering system 4. The superimposition steering system 4is connected to a steering gear 14 via an output shaft 12 of thesuperimposition steering system 4. The steering gear 14 can be embodied,for example, as a rack and pinion steering gear, as a recirculating ballgear or as a ball and nut gear. In the form of a rack and pinionsteering gear the steering gear 14 comprises, for example, a rack and apinion. The steering gear 14 is connected via the pinion and the rack toa corresponding steering linkage on each side of the vehicle, whichsteering linkage interacts with a wheel 16 in each case. Otherembodiments of the devices suitable for carrying out the methodaccording to the invention are conceivable. These embodiments can beconfigured, for example, by means of other steering gears or by means ofanother arrangement of the superimposition steering system 4 and thepower steering system 6.

Furthermore, a control device 18 is shown with which the superimpositionsteering system 4 and the power steering system 6 can be open-loopand/or closed-loop controlled. The control device 18 has a digitalcomputing device 20 in the form of a microprocessor and a memory 22. Acomputer program which is designed to carry out one of the methodsdescribed here can be stored in the memory 22. Correspondingly, thiscomputer program can be executed on the digital computing device 20. Ofcourse, instead of the control device 18 it is also possible for aplurality of control devices which are networked to one another to beprovided.

In a non-autonomous driving state, a wheel steering angle 24 occurs atthe wheels 16 of the vehicle as a function of the state of the steeringmeans 8. Depending on the position of the steering means 8 and/or of theinput shaft 10 a steering means angle 26 occurs. An angle 28 which isintroduced into the steering gear 14 results at the output shaft 12essentially by means of a transmission ratio into the wheel steeringangle 24. Consequently, the wheel steering angle 24 and the angle 28 canbe used here in an exchangeable fashion with one another.

A coupling 30 between the steering means angle 26 and the angle 28 whichis introduced into the steering gear 14 can be adjusted with thesuperimposition steering system 4. Increasing the coupling 30 meansreducing a relative movement of the input shaft 10 with respect to theoutput shaft 12. Reducing the coupling 30 means, on the other hand,increasing the relative movement of the input shaft 10 with respect tothe output shaft 12. By adjusting the coupling 30 it is thereforepossible, for example in the case of a fully autonomous driving mode, toadjust the wheel steering angle 24 by means of the power steering system6, wherein the steering means 8 does not move. Of course, completetracking of the steering means 8, that is to say essentially synchronousrunning of the shafts 10 and 12, can also be made possible in theautonomous driving mode, wherein, however, the coupling 30 isimmediately reduced in the event of an intervention by the driver intothe steering means 8, but it can be increased again in the event ofcontinuous intervention by the driver into the steering means 8.

A driver intervention 40 can be detected, for example, by means of asensor 42 on the steering means 8. In another embodiment, the driverintervention 40 can also be detected within the control device 18 fromother measurement variables and/or from detected variables which arepresent in the control device 18. Consequently, the sensor is to beunderstood as merely an example for the detection of the driverintervention 40.

In the fully autonomous driving mode or driving state of the vehicle,the wheel steering angle 24 is influenced as a function of a steeringtorque introduced via the power steering system 6, as a function of anautonomous steering function, running on the control device 18, withouta driver intervention 40. Therefore, a fully autonomous driving state ofthe motor vehicle is to be understood as meaning a driving state of themotor vehicle in which the driver does not engage in the steering means8 in order to obtain control over the vehicle but instead the entirecontrol over the vehicle or over the steering system 2 is exercised bythe autonomous driving function. In contrast, a partially autonomousdriving state of the motor vehicle or of the steering system is to beunderstood as meaning a state in which a driver intervention 40 isoccurring and in which the control over the vehicle is transferredeither from the driver to the autonomous steering function or from theautonomous steering function to the driver. Therefore, if the driverintervention 40 is detected for the first time in the fully autonomousdriving state, the vehicle goes into the partially autonomous drivingstate in which the driver intervention 40 has an effect on the wheelsteering angle 24 via the correspondingly adjusted coupling 30.

FIG. 2 shows a schematic state transition diagram with the fullyautonomous driving state 44, a first partially autonomous driving state46 and a second partially autonomous driving state 48 in the region 50.Starting from the partially autonomous driving state 46 it is possibleto change into a non-autonomous driving state 52 in which an autonomousdriving function does not actively or does not have any influence on thewheel steering angle 24. Consequently, the partially autonomous drivingstates 46 and 48 can each be denoted also as transient states, whereinby means of the transient state 46 it is possible to change from a fullyautonomous driving state to the non-autonomous driving state 52. Bymeans of the transient state 48 it is possible to change from thenon-autonomous driving state 52 into the fully autonomous driving state44. In the transient state 46 there is provision to increase thecoupling 30 in response to a driver intervention 40 in order thereforeto give the driver more control over the vehicle. In the transient state48 there is provision to give the driver less control and the autonomoussteering function more control in response to a reduced driverintervention 40. It is possible to change back and forth between thetransient states 46 and 48 depending on the detected increasing orreducing driver intervention 40.

FIG. 3 illustrates in schematic form the relationship between the driverintervention 40 and the influence 54 of the autonomous driving functionon the wheel steering angle. In the transient state 46, for example, theinfluence 54 of the autonomous driving function is reduced, whereas atthe same time the driver intervention 40 is increased. In contrast, inthe transient state 48 the influence 54 of the autonomous drivingfunction is increased and the driver intervention 40 is reduced.

1. A method for operating a steering system (2) of a motor vehicle,wherein a steering means (8) is connected to a steering gear (14) via asuperimposition steering system (4), the method comprising: detecting,during an autonomous driving mode of the motor vehicle, a driverintervention (40) of the driver into the steering means, and operatingthe superimposition steering system (4) in such a way that a coupling(30) between a steering means angle (26) and an angle (28) which isintroduced into the steering gear (14) is adjusted as a function of thedetected driver intervention (40).
 2. The method as claimed in claim 1,wherein an autonomous steering function by means of which a wheelsteering angle (24) of the steering system (2) of the motor vehicle canbe influenced is active during the autonomous driving mode, and furthercomprising determining the influence of the autonomous steering functionon the wheel steering angle (24) as a function of the detected driverintervention (40).
 3. The method as claimed in claim 1, furthercomprising increasing the coupling (30) as a function of an increasingor consistently elevated driver intervention (40).
 4. The method asclaimed in claim 2, further comprising reducing the influence of theautonomous steering function on the wheel steering angle (24) as afunction of an increasing or constantly increased driver intervention(40).
 5. The method as claimed in claim 3, further comprising detectingthe increasing or constant increased driver intervention (40) at a firsttime, and wherein starting from the first time up to a second time thecoupling (30) is increased and/or the influence of the autonomoussteering function on the steering wheel angle (24) is reduced in such away that at or after the second time the autonomous steering functioncan be deactivated.
 6. The method as claimed in claim 1, wherein thecoupling (30) is reduced as a function of a reducing driver intervention(40).
 7. The method as claimed in claim 2, wherein the influence of theautonomous steering function on the wheel steering angle (24) isincreased as a function of a reducing driver intervention (40).
 8. Themethod as claimed in claim 6, wherein at a third time the reducingdriver intervention (40) is detected, and wherein starting from thethird time up to a fourth time the coupling (30) is reduced and/or theinfluence of the autonomous steering function on the wheel steeringangle (24) is increased in such a way that at or after the third timethe steering function has complete control over the steering system (2).9. The method as claimed in claim 2, wherein the coupling (30) isadjusted as a function of a current and/or planned setpoint torque inputinto the steering gear (14), which input is detected by the autonomoussteering function.
 10. The method as claimed in claim 5, wherein in thecase of an increased vehicle speed, the time period between the firsttime and the second time and/or the time period between the third timeand the fourth time is longer than in the case of a reduced vehiclespeed.
 11. The method as claimed in claim 1, wherein a differentiationis made between an intended driver intervention (40) and between anunintended driver intervention (40), wherein, in the case of an intendeddriver intervention (40) the coupling (30) is increased or maintained,and wherein in the case of an unintended driver intervention (40) thecoupling (30) is reduced.
 12. The method as claimed in claim 1, whereinan increase in the coupling (30) between the steering means angle (26)and the angle (28) which is introduced into the steering gear (14)reduces a relative movement of an input shaft (10) of thesuperimposition steering system (4) and of the output shaft (12) of thesuperimposition steering system (4), and wherein a reduction in thecoupling (30) between the steering means angle (26) and the angle (12)which is introduced into the steering gear (14) increases a relativemovement of the input shaft (10) of the superimposition steering system(4) and of the output shaft (12) of the superimposition steering system(4).
 13. The method as claimed in claim 1, wherein the driverintervention (40) constitutes a steering angle which is applied to thesteering means (8) by the driver of the vehicle and/or a torque which isapplied to the steering means (8) by the driver of the vehicle, andwherein the driver intervention (40) is detected as a function ofcalculated and/or measured variables.
 14. A computer program for adigital computing device (20), which computing device (20) is designedto detect, during an autonomous driving mode of a motor vehicle, adriver intervention (40) of a driver of the motor vehicle into asteering means, and operate a superimposition steering system (4) insuch a way that a coupling (30) between a steering means angle (26) andan angle (28) which is introduced into the steering gear (14) isadjusted as a function of the detected driver intervention (40).
 15. Acontrol device (18) for operating a steering system (2) of a motorvehicle, which control device (18) is provided with a digital computingdevice (20) configured to detect, during an autonomous driving mode of amotor vehicle, a driver intervention (40) of a driver of the motorvehicle into a steering means, and operate a superimposition steeringsystem (4) in such a way that a coupling (30) between a steering meansangle (26) and an angle (28) which is introduced into the steering gear(14) is adjusted as a function of the detected driver intervention (40).